Having a child takes a lot out of you. In order to get back to your post baby body, it takes multiple steps of changing exercises. Initially you want to make sure you ease back into exercise until 6 weeks out to let your body recover.
Once you feel good about lighter exercise, such as zumba or yoga, you can amp it up. Once your energy levels are recovering and you are getting into a pattern with parenting you can build up your cardio and endurance into the mix. Just make sure to stay hydrated and give your body some rest between.